Start-up procedure for hydrogenative reforming with noble metal catalysts



June 28, 1960 s c; HINDIN START-UP PRocEDukE FOR HYDROGENATIVE REFORMING WITH NOBLE METAL CATALYSTS Filed A ril 26, 1957 2 Sheets-Sheet 1 A PRESSURE TESTING DRYING OF B REACTOR C CATALYST LOADING D CATALYST DRYING COOLING E AND DE PRESSURING PRESSURING AND F REDUCING WITH HYDROGEN G CHARGING REACTANTS INVENTOR.

ATTORNEX June 28, 1960 s. G. HINDIN 2,943,044

START-UP PROCEDURE FOR HYDROGENATIVE REFORMING WITH NOBLE METAL CATALYSTS Filed April 26, 1957 2 Sheets-Sheet 2 N an F OH R NU On A we 4 N N Mnv H T A FW 0 Nw U 6m L R n. c M M 9 7 W M m mmvyox. Jazz] fem/d fizzdm a \lm h M M AT T OKNEK REACTOR OUTLET TEMPERATURE, F-

United States Patent START-UP PROCEDURE FOR HYDROGENATIVE REFOSRMING WITH NOBLE METAL CATA- LYST Saul Gerald Hindin, Claymont, Del., assignor to Houdry Pro'cess 'Corporation, Wilmington, Del., a corporation of Delaware Filed Apr. 26, 1957, Ser. No. 655,289

3 Claims. (Cl. 208-146) This invention relates in general to hydrogenative/dehydrogenative reactions and other catalytic processes carried out over noble metal catalysts, such as hydrogenative reforming for the purpose of upgrading naphthas to high octane motor gasolines. The invention is particularly concerned with the start-up procedure for such processes and is directed to such precautionary steps during the initial start-up period as will effectively overcome certain deactivating influences which normally may be encountered in the initial use of such catalysts.

It has been found that, when a dual-function catalyst containing platinum .is employed .to promote dehydrogenation, isomerization and cracking reactions in a reforming operation for the purpose of upgrading low-octane naphthas, it .is necessary to exclude or eliminate moisture and oxygen from the catalyst mass during the step of initially reducing the catalyst with hydrogen prior to its'first contact with the naphtha charge stream.

Commercial experience has shown that, in a reforming operation employing supported platinum catalyst, the presence of even a small partial pressure of moisture and of relatively small quantities of oxygen in the reaction Zone during the catalyst reduction step may result in such serious deactivation of the catalyst as to render it practically unsuitable for further use.

Catalytic reforming processes of the type to which the invention has particular application are carried out as a fixed-bed operation, generally employing a plurality of spherical or cylindrical reactor vessels operating in sequence. The reactors are commonly arranged in a train of three or more, one or more such trains being employed in a large-size unit.

Once the reforming unit has been placed in operation, its functioning is continuous and substantially automatic, the operation continuing until the unit is shut down for the purpose of regeneration or inspection and repair, or for removal of the spent catalyst and replacement with fresh catalyst.

The present invention is concerned primarily with the procedural steps of starting up the reforming unit, that is, preparing the reactor and associated equipment for onstream operation with the initial introduction of the hydrocarbon charge. For this reason, only such description of the over-all process will be given herein as may be necessary to an understanding of the novel features of the invention and, since the functioning of the process during the actual hydrocarbon conversion forms no part of the invention, the details of the conversion process will not be described herein.

In commercial practice the start-up of a catalytic hydrocarbon reforming unit is attended with certain difiiculties and dangers. Unless extreme precaution is exercised in conditioning the unit and the materials to be introduced therein, substantial damage may be caused to the equipment and to the catalyst. .Such damage may necessitate an untimely shutdown for repair of equipment or reice Patented June 28, 1960 stated above, a principal hazard in starting up a hydrocarbon reforming unit is the presence of either water or oxygen within the reaction zone while the catalyst is being reduced with hydrogen. Water, for example, may be present in the refractory insulating material employed to line the reaction chamber, principally as the result of an insufiicient preliminary drying-out procedure; or it may appear as free water inadvertently admitted to the reaction zone during the period when the catalyst bed is being formed or remaining as a residue after hydrostatic .testing; or it may occur as water of adsorption acquired by the catalyst in the period between its manufacture and its ultimate introduction into the reactor at the point of use.

As the noble metal catalyst is received for loading into the reactors, its active component, such as platinum, is normally in a combined state. The oxidized component is subsequently reduced; with hydrogen during the startup stage, that is, the period when the unit as a whole is being warmed up and the reactors are being readied for the initial introduction of the hydrocarbon charge which places the unit on stream.

In view of the known deleterious effect of moisture within the reaction chamber during the period of catalyst reduction, certain procedural steps have generally been followed in commercial practice to preliminarily remove substantially all traces of Water. a

In any case, preliminary drying is generally required to remove traces of water remaining after the hydrostatic tests. If, as in some commercial units, the reactor vessel has been lined with refractory insulating material, there is additional reason for the drying out period during which the reaction chamber is heated and evacuated to carry off the water contained in the castable material or derived from the bonding material applied with the tiles. :Such initial drying step is carried out with sufiicient care to substantially preclude the presence of any remaining moisture in the reactor vessel at the time of catalyst loading.

When .the catalyst employed in the hydrocarbon reforming operation is hygroscopic in nature, the loading of the reactor to form the fixed compact bed of catalyst comprising the reaction zone is usually carried out at such time and under such conditions that the catalyst willnot be able to pick up any substantial amount of water. To this end, catalyst loading is generally performed during periods when there .is no actual precipitation, and the catalyst is not exposed to the air for any period longer than is necessary to complete such loading.

It has been found that despite these precaution-s, there.

may still be retained in the catalyst sufficient water, such as water of adsorption, to adversely elfect the activity of.

carbon charge stream. Commercial experience has shown that water so occurring, or perhaps accompanying the commercial hydrogen which is generally employed, at least in part, during the initial reduction step has in some cases been sufficient to cause substantial deterioration of the catalyst, principally in the form of deactivation. While'precaution is usually taken to obtain hydrogen that is relatively water-free, it is not equally easy to assure that the catalyst, as introduced into the reactor, does not contain amounts of water in excess of tolerable limits. 1

In accordance with the present invention, the catalyst, after being loaded into the reaction chamber, is subjected to a preliminary drying step under pressure and in the presence of hot inert gas, following which step the catalyst is cooled at lower pressure in preparation for purging and subsequent pressuring with hydrogen.

A preferred operation inaccordance with the inven;

3 tion will be described in connection with the accompanying drawings .forming a part of this application in which:

Fig. 1 is a diagrammatic illustration of the sequential steps comprising the preliminary heat treatment of freshly charged catalyst; and

Fig. 2 is a graph showing the criticality of temperature control during the warming up period.

In Fig. l the procedural steps of the invention are set forth as legends, and are designated by the letters A, B, C, .D, E, F and G.

Certain of the initial steps, such as A and B, may be necessary only when the reactor train is placed in service for the first time or when moisture has been introduced during a shutdown period, as when the internal lining of refractory insulating material has been repaired or replaced during such shutdown period.

Step A comprises the pressuretesting of the several vessels which form the reactor train, together with associated major items of equipment. Although it is a general practice to hydrostatically shop-test such equipment at higher than designed operating pressures so as to reveal any structural defects; or, in some cases, to hydrostatically field-test certain portions of the equipment, it is nevertheless desirable to put a gas test on the reactor section before loading with fresh catalyst in order to test for possible leaks. Such gas testing may comprise the introduction of air into the reactor vessel, for example at about 275-300 p.s.i.g. where suitable means for pressuring the air is available. If any leaks are found, they are repaired, which may require depressuring of the reactor, and the reactor section is again pressure tested.'

Step B involves a drying-out procedure which is generally employed before the reactor section is loaded with catalyst, in order to remove any water which may have accumulated in the equipment during hydrostatic testing in the field or which may be contained as adsorbed moisture in the materials employed to line the reactor vessels. In this step either air or inert gas may be used, although the latter may in some cases be preferred because air would cause some rusting of the internal portions of the equipment. The reactor section is first pressured with the desired drying gas at anywhere from about to several hundred p.s.i.g., and the gas is then circulated while being slowly heated until the reactor inlet temperatures are about 450 F. Preferably, the heating rate should not exceed about 50 F./hour. Continuous circulation of the drying gas is maintained until such time as the reactor outlet temperatures are at least 350 F., and in some cases in excess of 700 F., and there is no water present at any of the draw-off locations. The source of heat is then removed from the gas stream and gas circulation is continued until the reactor has cooled down to a temperaturebelow 250 F., and usually below 200 F. The reactor is then ready to be opened for catalyst loading.

Step C involves the operation of charging the desired amount of catalyst into the reactor and arranging the same as a fixed bed. Since the catalyst is hygroscopic, it should not be exposed to wetting or to moisture conditions during the loading operation for any period longer than is actually necessary. This precaution applies also to the loading into the reactor of other materials, such as inert alumina balls, to be used in the makeup of the catalyst bed. The loading should be completed and the reactor should be rescaled as quickly as possible.

a The fresh catalyst charged to the reactors would now, under ideal conditions, be ready for the reduction step, inasmuch as the catalyst, as normally received, would be in an oxidized condition. It is possible, however, that the catalyst may have been given a reduction treatmentin the final stage of manufacture, in which case it may not be quite as susceptible to deterioration in the presence of water or oxygen during the reduction step which preferably is carried out regardless of such prereduction treatment. It is at this precise point, however, that difficultieshave heretofore been experienced in direetly carrying out the reduction step, in large part by reason of the fact that a certain amount of moisture was introduced into the reactor with the new catalyst, either as moisture acquired duringthe loading operation or as adsorbed moisture acquired during storage and transportation from the point of manufacture to the point of use, or was formed therein as a result of oxygen being introduced as an impurity with the hydrogen. To eliminate the introduced water, there is provided a preliminary catalyst drying step immediately preceding the catalyst reduction step, thereby preventing any serious deactivation of the catalyst during such reduction step resulting from the presence of water in the catalyst as introduced into the reactor.

Step D involves a drying procedure which consists of heating the catalyst to ajtemperature not in excess of about 900 F. with circulating inert gas at a pressure in the range of about -200 p.s.i.g. The rate of heating is carefully controlled so as generally not to exceed about 50 F./ hour. Precautions should be taken to see that the drying gas is relatively free of either hydrogen or carbon monoxide, since the latter also is harmful to the catalyst at temperatures within the drying range, and the presence of hydrogen would cause reduction of the catalyst while wet.

When the drying gas is circulated through a reactor bed the initially contacted portion of the bed tends to saturate the circulating gas with moisture, that is, in those cases where there is any appreciable amount of moisture adsorbed in the catalyst. If there is a substantial temperature drop through the reactor there is a likelihood that the moisture will recondense on the catalyst parti cles forming the lower portion of the catalyst bed. Obviously, where a train of reactors is being dried in a single operation by passing the circulating gas in series through the plurality of reactors this effect may be additive from one reactor to the next. It is therefore important that an excessive temperature drop be avoided through any of the series of reactors. To prevent such condition, each successive reactor of a train of reactors is maintained somewhat hotter than the preceding reactor. Any problem with respect to recondensation is avoided by controlling the rate of heating during the catalyst drying step in accordance with the graph shown in Fig. 2 of the drawings. Suflicient legends are incorporated in the drawing to make the graph self-explanatory.

Step E involves the cooling and depressuring of the reactor after it has been subjected to the action of the circulating stream of drying gas to the point where no more water can be removed. First, the source of heat is removed from the circulating gas stream and the gas continues to be circulated until the reactor is cooled down to a temperature, such as about 200 F., at which it is considered safe to add hydrogen or other combustible gas, as in the next step.

While such gradual cooling is being elfected, or immediately thereafter, the pressure is bled oif so as to depressure the reactor.

Step F involves a repressuring of the reactor and reduction of the catalyst with hydrogen, immediately prior to which, however, the reactors are purged. For the initial start-up of a reactor purchased hydrogen may need to be used to pressure the reactor, after which the necessary hydrogen may be derived from the process. Since oxygen, as well as moisture, has a serious deactivating effect upon the catalyst during the reduction step, it is essential that relatively pure hydrogen be employed for such purpose. In purchasing hydrogen, therefore, it is desirable that the oxygen content of the hydrogen be less than 0.05%. When the subsequent operation of the unit is carried out with hydrogen produced in the reforming process, there is no need for concern about the oxygen content of the hydrogen recycle gas stream because such hydrogen stream contains no oxygen.

With reference to the aforementioned purge, before the hydrogen is introduced into the reactor, one or more inert gas purges must be employed to clear the reactor of any remaining undesirable gaseous material. The reactor is then evacuated to 26" Hg vacuum andis carefully tested for leaks by vacuum loss. If the reactor is satisfactorily gas-tight, hydrogen is then introduced to break the vacuum to 2-3 p.s.i.g. The reactor is then again evacuated to 26" Hg vacuum. This step of breaking the vacuum and evacuating is again repeated, following which the reactor is again pressured with hydrogen, for example, to a pressure up to about 50-100 p.s.i.g. The hydrogen-pressured reactor is then slowly heated in accordance with the curve of Fig. 2 to a temperature of about 350-400 F., with the pressure in the reactor being maintained at a level not to exceed about 100 p.s.i.g. The reactor is then further pressured with hydrogen to a final pressure in the range of 300-500 p.s.i.g., while the reactor inlet temperature is gradually adjusted to about 775 F. The reactor is now ready to receive the hydrocarbon charge.

Step G involves the introduction of the naphtha charge into the reactor, the reactants being'rnade to flow as a continuous stream through the catalyst bed. In a typical reforming operation a plurality of reactors will be employed and will be connected in series. When fresh catalyst is used, there may be a marked temperature rise of about 50-75 F. in the reactor when the naphtha first contacts the new catalyst. During this initial period of adjustment, extreme care is exercised to see that the reaction temperatures do not become too high or too low. After a short time, the temperature fluctuations level off, and it is then possible to raise the reactor inlet temperature to a normal operating level, such as 800975 F., at which higher temperatures the reactor will produce hydrogen gas which will then be available for recycle.

Operations beyond this point will depend upon the specifications of the particular unit. Since the invention is primarily concerned with the initial start-up procedure, they will not be described.

By the start-up procedure of the present invention it is possible to assure that the noble metal catalyst, from the time of its initial introduction into the reactor to the time of its initial contact with the hydrocarbon charge stream, will be free from contact with materials which under the prevailing conditions may react with the noble metal, and that the treating zone will be kept relatively free of materials which under the same conditions may have an adverse effect upon the internal surface portions of the reactor within the treating zone.

Thus, with respect to the protection of the catalyst during the drying step, the invention contemplates that the so-called inert drying gas will be relatively free of such materials as hydrogen or carbon monoxide, the former of: which would cause p-re-reduction of the catalyst in the presence of the harmful material (moisture) which it is desired to remove before the actual reduction step, and the latter of which might be harmful to the catalyst at any time.

The invention contemplates that air may be employed as the drying gas although it is recognized that the presence of the oxygen component during the high-temperature drying period may cause some undesirable rusting of the internal surfaces of the equipment.

It is therefore to be understood that for the purposes of this invention the expression inert gas, as used herein, shall mean such gas or gaseous mixture as will be relatively free of deleterious materials, such as hydrogen, or carbon monoxide. Such gas may comprise, for example, nitrogen, natural gas, etc.

Since the method of the present invention makes it possible to eliminate from the reaction zone during the period of catalyst reduction with hydrogen substantially all moisture, whether derived from the lining materials or from the catalyst itself, there is thus removed any serious danger of catalyst deterioration from such sources. It is assumed ofcourse that other precautions will have been taken to see that there is substantially no oxygen present in the reaction zone while the reduction treatment is being effected, the presence of which has been recognized as another cause of catalyst deterioration;

'To determine the effects of pressure, oxygen and water on catalyst activity of noble metal catalysts during reduction, a series of experiments was carried out on commercial activated alumina pellets treated with 10% acetic acid solution for one hour, decanted, and the treat: ment repeated for another hour with fresh acid of the same concentration, employing an amount of acid-just sufiicient to cover the pellets. The treated pellets were then washed at number of times with water, dried at 240 F. and calcined in air at 900 F. The calcined pellets were then dipped for one hour in a chloroplatinic acid solution of suflicient strength to give about 0.6% by weight of platinum on the finished catalyst. The impregnated catalyst was then dried at 240 F. and, on analysis, the finished catalyst was found to contain 0.5% by weight of platinum.

In the experiments, a reduction of the catalyst was carried out at varying pressures up to 300 p.s.i.g and with varying degrees of oxygen concentration (up to- 1.0 mole percent) in the hydrogen during the reduction treatment. Oxygen was added to the hydrogen both as gaseous oxygen and as water.

The effects of pressure and the presence of oxygen during the reduction treatment of the catalyst was then determined by measuring the platinum activity of the reduced catalyst. This was accomplished by tests in which cyclohexane was converted to benzene.

The activity of a catalyst in promoting dehydrogenation can be readily measured by conversion of cyclohexane thereover under standardized conditions. The test. employed in evaluating the several catalysts hereinafter described was carried out by passing a pure grade of cyclohexane (n =l.4260) over a 5 cc. sample of the catalyst during a thirty-minute run period, at atmospheric pressure, at a temperature of 650 F.,. and at a liquid hourly space velocity of 6 volumes of the hydrocarbon per volume of catalyst; hydrogen was added to the charge at the rate of 4 mols per mol of the cyclohexane. Observed deviations in temperature from the 650 F. standard were corrected by reference to an established table of temperature-conversion relationships. The activity of the catalyst is expressed as percent.benzene produced from the charge as measured. by the refractive index of the liquid condensate. At these operating conditions the reaction is highly selective and no products other than cyclohexane, benzene and hydroge are found in the reactor effluent.

As to the effect of pressure, it was found that the platinum activity is greatest when reduction is carried out at atmospheric pressure, and decreases with increasing pressure up to 300 p.s.i.g. The decrease in activity is linear with pressure, and equals about 6 cyclohexane numbers per p.s.i.g. It was found that little, if any, further decrease in activity occurs when the reduction pressure is increased to 600 p.s.i.g.

As to the elfect of oxygen content of the hydrogen during reduction, it was found that platinum activity is greatly decreased when the catalyst is reduced with hydrogen containing oxygen at pressures of about 300 p.s.i.g., similar to those commonly used in commercial start-ups. The decrease in activity is linear in the range of 00.3 mole percent oxygen, and equals 5 cyclohexane numbers per 0.1 mole percent oxygen. The presence of oxygen in amounts greater than 0.4 mole percent, and up to 1.0 mole percent, does not further reduce activity.

As to the effect of water content of the hydrogen during reduction, water present in the hydrogen during the reduction causes serious platinum deactivation. The extent of this deactivation increases with increase in reduction pressure, both at constant mole percent water and at constant partial pressure of water. In addition, at constant reduction pressure the extent of deactivation increases with increasing water concentration. At 300 p.s.i.g., reduction in the presence of 0.2 mole percent of water gives a cyclohexane number decrease in activity.

It appears that a given amount of oxygen causes the same amount of deactivation, whether present as gaseous oxygen or as water.

By starting up a catalytic reforming unit of the type herein described in accordance with the procedure of the present invention, that is, by providing a catalyst preheating step immediately preceding the catalyst reduction step, and by employing an inert and non-reducing gas, under the conditions stated, to effect the desired drying, it is possible to substantially eliminate the presence of water within the reactors during reduction. Deactivation of the noble metal catalyst during the process of initially preparing the catalyst bed to receive the hydrocarbon charge is therefore avoided.

While but one mode of carrying out the process of the invention has been described, it will be obvious to those skilled in the art that the invention is susceptible to various modifications without departing from the spirit of the invention, and it is desired therefore that only such limitations shall be placed thereon as are imposed by the appended claims.

What is claimed is:

1. A start-up procedure for initiating with fresh catalyst hydrocarbon conversion processes involving hydrogenative/dehydrogenative reactions carried out in the presence of a mass of granular noble metal catalyst maintained as a fixed bed within a treating zone, which comprises the preliminary steps of: initially drying out said treating zone; introducing the fresh, as-received catalyst into said treating zone to form said bed; heating said bed of catalyst to a temperature suitable to effect the desired drying, but not in excess of about 900 F., by circulating hot gaseous material substantially free of hydrogen and carbon monoxide through said bed at apressure in the range of about 50-200 p.s.i.g. and at such controlled rate that the temperature differential between the regions of highest and of lowest temperature will not be great enough to effect a recondensation of moisture in any region of said bed; removing the source of heat from the circulating stream of gaseous material when no more water is being removed from said catalyst; continuing said circulation of gas through said bed until said treating zone is cooled down to a temperature which will allow for any reasonable temperature surge which may possibly occur during subsequent reduction; depressuring said treating zone; purging said treating zone with inert gas and evacuating to vacuum; breaking said vacuum with hydrogen and again evacuating; pressuring said treating zone with hydrogen up to about 50-100 p.s.i.g.; slowly heating said catalyst to a temperature of about BSD-400 F. while maintaining said pressure at not more than about 100 p.s.i.g.; further pressuring said treating zone with hydrogen to a final pressure in the range of 300-500 p.s.i.g. while gradually adjusting the gas inlet temperatureof said treating zone to about 775 F.; introducing the hydrocarbon charge into said treating zone as a continuous stream flowing through said bed; and, after temperature fluctuations incident to the initial contacting of said charge with the fresh catalyst have leveled off, gradually raising the temperature of said treating zone to the desired operating level.

2. In the initial start up with fresh catalyst of a catalytic hydrocarbon conversion process wherein hydrogenative-dehydrogenative reactions are carried out Within a reactor in the presence of a fixed bed of noble metal catalyst which has first been partially reduced, in which start up procedure said reactor, before loading with catalyst to a temperature not in excess of about 700 F., the rate of said catalyst drying being contained in the materials of construction, the improvement which comprises the preliminary steps of: drying said catalyst after said loading by circulating a heated stream of non-reducing inert gas, substantially free of hydrogen and carbon monoxide, through said bed at a pressure in the range of about 50-200 p.s.i.g., to thereby heat said catalyst to a temperature not in excess of about 700 F., the rate of said catalyst drying being controlled so that the temperature differential between the regions of highest and lowest temperature within said reactor will not be great enough to effect a recondensation of moisture therein; removing said water from said circulating stream of inert drying gas; removing the source of heat from said stream of drying gas While continuing its circulation until said catalyst is cooled to a temperature substantially below 350 F.; depressuring said reactor; purging said reactor with inert non-reducing gas and evacuating to vacuum; pressuring said reactor with hydrogen and slowly heating said catalyst to a temperature of about 350-400 F., while maintaining a pressure of not more than about p.s.i.g.; further pressuring and heating said reactor with hydrogen to a final pressure of about 300-500 p.s.i.g. and a gas inlet temperature of about 775 F., introducing the hydrocarbon charge to said reactor as a continuous stream; and thereafter gradually raising the temperature of the reactor to the desired operating level.

3. A method as in claim 2, in which the rate of heating.

of said catalyst during said drying with a heated stream of non-reducing inert gas does not exceed about 50 F./hr.

References Cited in the file of this patent UNITED STATES PATENTS 2,266,033 Harrison Dec. 16, 1941 2,266,095 Thayer Dec. 16, 1941 2,388,536 Gunness Nov. 6, 1945 2,743,215 Riblett et al. Apr. 24, 1956 2,773,013 Wolf et al. Dec. 4,1956 2,773,014 Snuggs et al Dec. 4, 1956 CERTIFICATE OF CORRECTION Patent Noa 2,94S O44 June 28 .1960 Saul Gerald Hindin Column 8, lines 16 and 17 strike out, to a temperature not iu excess of about 700 F. a the rate of said catalyst drying being" and substitute is subjected to preliminary drying for (SEAL) Attest:

ERNEST- sW'DER ARTHUR W. CROCKER Attesting Uflicer A ti Commissioner of Patents 

1. A START-UP PROCEDURE FOR INITIATING WITH FRESH CATALYST HYDROCARBON CONVERSION PROCESSES INVOLVING HYDROGENATIVE/DEHYDROGENATIVE REACTIONS CARRIED OUT IN THE PRESENCE OF A MASS OF GRANULAR NOBLE METAL CATALYST MAINTAINED AS A FIXED BED WITHIN A TREATING ZONE, WHICH COMPRISES THE PRELIMINARY STEPS OF: INITIALLY DRYING OUT SAID TREATING ZONE, INTRODUCING THE FRESH, AS-RECEIVED CATALYST INTO SAID TREATING ZONE TO FORM SAID BED, HEATING SAID BED OF CATALYST TO A TEMPERATURE SUITABLE TO EFFECT THE DESIRED DRYING, BUT NOT IN EXCESS OF ABOUT 900*F., BY CIRCULATING HOT GASEOUS MATERIAL SUBSTANTIALLY FREE OF HYDROGEN AND CARBON MONOXIDE THROUGH SAID BED AT A PRESSURE IN THE RANGE OF ABOUT 50-200 P.S.I.G. AND AT SUCH CONTROLLED RATE THAT THE TEMPERATURE DIFFERENTIAL BETWEEN THE REGIONS OF HIGHEST AND OF LOWEST TEMPERATURE WILL NOT BE GREAT ENOUGH TO EFFECT A RECONDENSATION OF MOISTURE IN ANY REGION OF SAID BED, REMOVING THE SOURCE OF HEAT FROM THE CIRCULATING STREAM OF GASEOUS MATERIAL WHEN NO MORE WATER IS BEING REMOVED FROM SAID CATALYST, CONTINUING SAID CIRCULATING OF GAS THROUGH SAID BED UNTIL SAID TREATING ZONE IS COOLED DOWN TO A TEMPERATURE WHICH WILL ALLOW FOR ANY REASONABLE TEMPERATURE SURGE WHICH MAY POSSIBLY OCCUR DURING SUBSEQUENT REDUCTION, DEPRESSURING SAID TREATING ZONE, PURGING SAID TREATING ZONE WITH INERT GAS AND EVACUATING TO VACUUM, BREAKING SAID VACUUM WITH HYDROGEN AND AGAIN EVACUATING, PRESSURING SAID TREATING ZONE WITH HYDROGEN UP TO ABOUT 50-100 P.S.I.G., SLOWLY HEATING SAID CATALYST TO A TEMPERATURE OF ABOUT 350-400* F. WHILE MAINTAINING SAID PRESSURE AT NOT MORE THAN ABOUT 100 P.S.I.G., FURTHER PRESSURING SAID TREATING ZONE WITH HYDROGEN TO A FINAL PRESSURE IN THE RANGE OF 300-500 P.S.I.G. WHILE GRADUALLY ADJUSTING THE GAS INLET TEMPERATURE OF SAID TREATING ZONE TO ABOUT 775*F., INTRODUCING THE HYDROCARBON CHARGE INTO SAID TREATING ZONE AS A CONTINUOUS STREAM FLOWING THROUGH SAID BED, AND, AFTER TEMPERATURE FLUCTUATIONS INCIDENT TO THE INITIAL CONTACTING OF SAID CHARGE WITH THE FRESH CATALYST HAVE LEVELED OFF, GRADUALLY RAISING THE TEMPERATURE OF SAID TREATING ZONE TO THE DESIRED OPERATING LEVEL. 